The present invention relates to manually operated self-contained strapping tools for joining overlapping portions of thermoplastic strap meterial by the friction-fusion technique.
Prior art strapping tool devices are commonly disclosed as being powered by pneumatic or electric motors. See U.S. Pat. No. 3,442,733 to Vilcins and U.S. Pat. No. 3,586,572 to Ericsson. It can be appreciated, however, that a need exists for a more versatile strapping tool that is completely self-contained for those situations where a suitable source of air or electricity is not available. Self-contained manual strapping tools have been developed, but have the drawback that a high energy input is needed for sealing in a single stroke. Such a manual strapping tool is illustrated in U.S. Pat. No. 3,442,734 to Ericsson and utilizes a floating gripper shoe which is driven by a coil-spring actuated cam. The coil spring is compressed by a power cylinder or a bell crank to initiate the sealing cycle.
Another self-contained manually operated strapping tool for receiving overlapping portions of thermoplastic strap formed into a loop about an article is disclosed in German Published Specification No. 1,923,907. This particular tool includes a movable jaw mounted on a rotatable eccentric that is spring loaded so as to bring the movable jaw in close proximity to an opposing fixed jaw. A locking mechanism is associated with the movable jaw to hold it in a position remote from the fixed jaw so that overlapping strap portions can be inserted and removed from between the jaws. An actuating lever is reciprocatingly cranked to drive a ratchet feed wheel unit to pull tension on the strap loop and at the same time to wind a driving spring to tension. With the loop under tension, the actuating lever is pivoted to release the spring loaded eccentric to bring the movable jaw close to the fixed jaw and compress the overlapping strap portions. The actuating lever is again pivoted to release the tensioned driving spring which acts to spin a driver shaft for a short period of time. A star wheel having arcuate portions positioned end-to-end around the circumference of the wheel is fixedly attached to the driver shaft and rotates as the shaft is spun. A rocker, positioned adjacent to the periphery of the star wheel, is oscillated back and forth by the arcuate surface portions of the star wheel as it is rotated. The movable jaw is coupled to the rocker so that it also oscillates causing the interface regions of the compressed overlapping strap portions to melt. A cutter mechanism is subsequently actuated by another handle to sever the upper strap from a supply strap. Thereafter, the actuating lever is pivoted to separate the jaws and release the strap from engagement by the tool.
The strapping tool disclosed in the foregoing publication constitutes a quite intricate and costly piece of equipment. Not all users of strapping tools have needs that wuld necessitate the expense of such a tool. Thus it is desirable to provide a less costly manual strapping tool that is completely portable, of lightweight, simple and compact design, and a tool that requires a relatively low energy input for effective sealing.